Over the past ten years, the fast expansion and evolution of all kinds of digital media has brought with it significant advancement and standardization of, among other things, the MPEG video compression algorithm and associated file format for a corresponding saving in content storage and delivery bandwidth. The MPEG family of standards includes MPEG-1, MPEG-2 and MPEG-4, respectively formally known as ISO/IEC 11172, ISO/IEC-13818 and ISO/IEC-14496. Chronologically, MPEG1 was introduced in 1988 with a data rate 1.5 Mb/sec (Megabits/sec) and primarily used for VCD applications; MPEG2 was born in early 1990s with a data rate >3.0 Mb/sec and used extensively for multimedia applications; MPEG4 was introduced in 1995 for video based applications; and, currently, MPEG7 is the latest technology and used for video database applications.
Of particular importance is the by-now commercially well accepted industry standard MPEG2. In fact, as the MPEG2 has been so stabilized in terms of adoption by the mass market, in addition to numerous software tools being made available for its implementation, there were also emergence of corresponding integrated Circuits (IC) performing such related functions in hardware. One example is the M65727FP MPEG2 MOTION ESTIMATION LSI made by Mitsubishi Electric Corporation.
A commonly accepted measurement of the effectiveness of a video compression algorithm when applied to a video title is Video Compression Ratio (VDCR), defined as follows:VDCR=Raw Data/Encoded DataWhere Raw Data, expressed in Gigabytes (GB), is the total amount of digital data required to store the video title at a fixed image display resolution with no video compression. For example, under an NTSC standard, the fixed image display resolution for a consumer-quality video is 352×240 pixels. After the compression by the video compression algorithm, the same video title now only requires Encoded Data, also expressed in GB, for storage. It follows that a more effective video compression algorithm should provide a higher VDCR. Of course, as always, all applications of any video compression algorithm must produce a corresponding Video Image Quality (VDIQ) that is acceptable and should be as good as possible. Under a typical application of MPEG2, a VDCR in the range of 20–30 is achievable with acceptable VDIQ.
Upon closer inspection of the MPEG2 specification, however, it is noticed that significant latitude in the selection of mode of compression and recommended range of compression control parameters is available for a set of parameters called MPEG2 Control Parameters (MPCP). For convenience of illustration, the MPCP, typically adopted by current DVD suppliers in the market, are presented in TABLE I below together with their mode and range of compression.
TABLE ITypical MPEG2 Control Parameters (MPCP)Typical range adopted by currentMPCPDVD suppliersSet Video Size used by DVD:35–50 × (Minutes of Video) likely(x Value) × (Minutes of Video)set via file size of a DVD titleMaximum BITRATE used by DVD7500–15000Maximum AverageAverage BITRATEBITRATE/Average BITRATE used4000–9500by DVDMinimum BITRATE used by DVD0
While TABLE 1 illustrates the mode and range of compression generally associated with the MPCP typically adopted by current DVD suppliers, little is revealed as to how such range is ultimately selected for the MPCP to achieve a higher VDCR with a desirable VDIQ. In particular, little has been shown as to how the VDCR and VDIQ of a video title could be affected when the corresponding MPCP is adjusted in a systematical and simultaneous manner.
Significantly, it is found by the present invention that as the value of MPCP is adjusted within their adopted ranges according to TABLE I, the VDCR and VDIQ of the resulting MPEG2 file exhibit a correspondingly significant variation according to the present invention. Even more surprisingly, drastic improvement of the VDCR has been observed from certain out-of-range adjustments of the MPCP.
Therefore, by systematically and simultaneously adjusting the MPCP, an opportunity exists for simultaneous achievement of a significantly higher VDCR than that is available from the current DVD suppliers in the art while still maintaining a comparable or even achieving a better VDIQ.